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FreeBSD-SA-20:15.cryptodev                                  Security Advisory
                                                          The FreeBSD Project

Topic:          Use after free in cryptodev module

Category:       core
Module:         cryptodev
Announced:      2020-05-12
Credits:        Yuval Kanarenstein
Affects:        All supported versions of FreeBSD.
Corrected:      2020-01-20 11:19:55 UTC (stable/12, 12.1-STABLE)
                2020-05-12 16:57:47 UTC (releng/12.1, 12.1-RELEASE-p5)
                2020-01-20 11:19:55 UTC (stable/11, 11.3-STABLE)
                2020-05-12 16:57:47 UTC (releng/11.3, 11.3-RELEASE-p9)
CVE Name:       CVE-2019-15879

Note: The upcoming release of FreeBSD 11.4 was branched after the original
commit to the stable branch and already includes the fix for this advisory.

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I.   Background

The cryptodev module permits userland applications to offload
cryptographic requests to device drivers in the kernel.  Applications
create sessions via file descriptors opened from /dev/crypto.

II.  Problem Description

A race condition permitted a data structure in the kernel to be used
after it was freed by the cryptodev module.

III. Impact

An unprivileged process can overwrite arbitrary kernel memory.

IV.  Workaround

Unload the cryptodev kernel module if it is loaded:

# kldunload cryptodev

Note that the cryptodev module is not loaded by default and is not
used by most applications.  Specificially, use of accelerated software
cryptography, such as AES-NI, in userland applications via libraries such
as OpenSSL do not make use of the cryptodev module.

V.   Solution

Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date, and
reboot the system.

Perform one of the following:

1) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for a security update"

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 12.1]
# fetch https://security.FreeBSD.org/patches/SA-20:15/cryptodev.12.patch
# fetch https://security.FreeBSD.org/patches/SA-20:15/cryptodev.12.patch.asc
# gpg --verify cryptodev.12.patch.asc

[FreeBSD 11.3]
# fetch https://security.FreeBSD.org/patches/SA-20:15/cryptodev.11.patch
# fetch https://security.FreeBSD.org/patches/SA-20:15/cryptodev.11.patch.asc
# gpg --verify cryptodev.11.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/12/                                                        r356908
releng/12.1/                                                      r360976
stable/11/                                                        r356908
releng/11.3/                                                      r360976
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-15879>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-20:15.cryptodev.asc>
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